The invention relates generally to a cryogenic dielectric environment for high temperature superconductor (HTS) devices and more particularly to high voltage structures in a cryogenic dielectric environment for an electrical power system.
As the need for higher power and higher voltage applications of Superconducting devices increases, designing high voltage devices in a cryogenics dielectric environment becomes a challenge. The cryogenic dielectric systems are not yet well understood as viable insulation systems for high voltage applications. Conventional high voltage devices such as high voltage cables have employed corona shields to control electrical field stress, however, electrical corona shield solutions have not been employed in a cryogenic environment
For example, U.S. Pat. No. 4,705,918 teaches the use of a corona shield assembly connected to various portions of a transmission line subassembly having two sets of oppositely mounted corona shields, where each corona shield is bolted directly to a portion of the transmission line subassembly such that the corona shield extend substantially over the subassembly portion of the transmission line. This patent does not teach or disclose the use of a corona shield in a cryogenic environment.
Use of corona shields in test equipment has been described, for example, in the publication, “Pre-breakdown and breakdown phenomena in liquid nitrogen at high voltage, comparison with mineral oil”, O. Lesaint et. al., Workshop on Cryogenic Dielectrics, published Oct 16, 2005, Nashville Tenn. Intermediate plate insulation has also been disclosed in publications presented by the University of Southampton and KFK, O. Lesaint et. al., at the Workshop on Cryogenic Dielectrics, Oct 16, 2005, Nashville Tenn.
In another example, U.S. Pat. No. 5,488,199 teaches the use of an electrical stress controlled solid dielectric cable termination assembly having an electrical stress control device, which comprises a metal conductor shaped to achieve an electrical stress control function. A durable material having a high dielectric strength is applied as a coating to the exposed surfaces of the conductor. The coatings prevent conductive particles or contaminants, which may be present in an insulating fluid medium from directly contacting the stress control device. A corona shield is formed from a modified cylindrically shaped metal conductor. A partially conductive shield layer of the cable is properly terminated in an electrical stress reducing configuration by applying a partially conductive sleeve pre-finished in the desired shape to overlap the shield layer. This patent does not teach or disclose the use of a corona shield in a cryogenic environment. There is therefore a need to apply corona shield technology in cryogenic dielectric applications.